Semiconductor integrated circuit device

ABSTRACT

Into an internal circuit to operate in a high-frequency band, there is incorporated a protective circuit of a multistage connection which is constructed to include a plurality of diode-connected transistors having a low parasitic capacity and free from a malfunction even when an input signal higher than the power supply voltage is applied. Into an internal circuit to operate in a low-frequency band, there is incorporated a protective circuit which is constructed to include one diode-connected transistor. The protective circuits include two lines of protective circuit, in which the directions of electric currents are so reversed as to protect the internal circuits against positive/negative static electricities.

CROSS-REFERENCES

This is a continuation application of U.S. Ser. No. 11/104,541, filedApr. 13, 2005, now U.S. Pat. No. 7,298,600 which is a continuationapplication of U.S. Ser. No. 10/664,968, filed Sep. 22, 2003 (now U.S.Pat. No. 7,035,069), which is a continuation of Ser. No. 09/785,499,filed Feb. 20, 2001 (now U.S. Pat. No. 6,665,159).

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuitdevice and, more particularly, to a technique which is effective whenapplied, in a semiconductor integrated circuit device including circuitsfor processing signals from an intermediate-frequency band to ahigh-frequency band, to a protective technique for preventing theelectrostatic breakdowns of circuit elements constructing thesemiconductor integrated circuit device.

A wireless communication system (or a wireless communication mobileterminal device, as will be shortly called the “terminal device”) suchas a digital cellular system has its circuits of transmission line andreception line constructed to include many discrete ICs (semiconductorintegrated circuit devices). A representative example of the terminaldevice, of which the transmission/reception line circuits areconstructed of the discrete ICs, is shown in FIG. 9. The discrete ICsare serviced from semiconductor parts makers such as NEC or RF MicroDevice.

On the other hand, the technique of integrating thetransmission/reception units into one chip is described on pp. 17 to 20of “Hitachi Review”, Vol. 81, No. 10 (1999-10), issued by HitachiReviewer Co., Ltd.

On the other hand, the electrostatic breakdown protecting circuit of ICis disclosed in Japanese Patent Laid-Open No. 230266/1989, for example.In this Laid-Open, there is disclosed an electrostatic breakdownpreventing circuit in which a plurality of diodes are connected inseries between the terminal of an integrated circuit and a power supplyline or a ground line.

In Japanese Patent Laid-Open No. 202583/1995, on the other hand, thereis disclosed a CMOS protective circuit corresponding to the CMOS circuitin which a plurality of power supply voltages are mixed.

Here will be described the prior art with reference to the accompanyingdrawings. FIG. 9 is a schematic block diagram showingtransmission/reception circuits or the like, which are packaged in theterminal device of the prior art. The ICs are individually madefunctionally discrete, and the portions, as individually enclosed bysquares, are the discrete ICs.

In this block diagram, there are shown a transmission line and areception line, which are connected with an antenna 1 through a duplexer2. Both these transmission line and reception line are connected withthe not-shown base band.

The reception line is constructed by connecting the antenna 1, aband-pass filter 3 packaged in the duplexer 2, a low-noise amplifier 4,a band-pass filter 5, a reception mixer 6, a band-pass filter 7, avariable-gain controlled amplifier 8 and a demodulator 9 sequentially inseries. The demodulator 9 is connected with the not-shown base band.

The transmission line is constructed by connecting a modulator 11, avariable-gain controlled amplifier 12, a transmission mixer 13, aband-pass filter 14, a transmission preamplifier 15, a high-outputamplifier 16, a band-pass filter 17 packaged in the duplexer 2, and theantenna 1 sequentially in series. The modulator 11 is connected with thenot-shown base band. On the other hand, the demodulator 9 and themodulator 11 perform the frequency conversion in response to a stationsignal inputted from a VCO 18. The reception mixer 6 and thetransmission mixer 13 also perform the frequency conversion in responseto the station signal from a VCO 19.

The signals (in electric waves) 10, as received by the antenna 1, aresequentially processed by the individual circuits of the reception lineand are sent to the base band. On the other hand, the signals, as sentfrom the base band, are sequentially processed by the individualcircuits of the transmission line and are emitted as the electric waves10 from the antenna 1.

The portions, as enclosed by the squares, are the discrete ICs, as hasbeen described hereinbefore. On the other hand, the internal smallsquares are electrostatic breakdown protecting circuits 20 (as will becalled the “protective circuits”).

In the construction of the prior art thus far described, it is estimatedfrom the handling notices described in the IC catalogue of eachsemiconductor parts maker that the variable-gain controlled amplifiers 8and 12, the demodulator 9 and the modulator 11, or theintermediate-frequency band ICs of several hundreds MHz are providedwith the protective circuits 20 for preventing the circuit breakdowns,as might otherwise be caused by the electrostatic charges from severaltens to several hundreds V, to enhance the high breakdown voltages.

On the other hand, the high-frequency band ICs in the vicinity of 1 GHzsuch as the low-noise amplifier 4, the reception mixer 6, thetransmission mixer 13, the transmission preamplifier 15 or thehigh-output amplifier 16 are described for the user to consider thestatic electricities, and it is also estimated that no protectivecircuit is included.

As one example of the protective circuit, there is known a protectivecircuit which is disclosed in Japanese Patent Laid-Open No. 202583/1995,as described hereinbefore. FIG. 10 is a schematic diagram in which aportion is added for easier illustration to the diagram of theprotective circuit presented by the Laid-Open.

In FIG. 10, numeral 41 designates a protective circuit. Letter Vdesignates an input or output signal to an integrated circuit, and thissignal is inputted via a signal line 44 to an internal circuit 45 oroutputted from the internal circuit 45. The protective circuit 41 ismade of a diode-connected NMOS transistor 42 and an NMOS transistor 43.Specifically, the transistor 42 is connected at its shorted gate anddrain with the signal line 44 and is connected at its source with apower supply voltage Vcc. On the other hand, the transistor 43 isconnected at its drain with the signal line 44 and at its shorted gateand source with the ground.

On the other hand, one example of the protective circuit having diodesconnected at multiple stages is disclosed in Japanese Patent Laid-OpenNo. 230266/1989, as has been described hereinbefore. FIGS. 11 and 12 areschematic diagrams in which a portion is added to the diagrams of thediodes for forming the protective circuit and the electrostaticbreakdown preventing circuit of that Laid-Open, so as to facilitate thedescription.

As shown in FIG. 11, two diodes 51 and 52 are connected in series at twostages in the forward direction between the signal line 53 and theground line 55 of an internal circuit 54. A signal is transmitted viathe signal line 53 to the internal circuit 54. FIG. 11 omits theprotective circuit on the power supply side, the action of which isidentical to that shown in FIG. 10.

By the two-stage construction, a Von voltage is raised to suppress theelectric current to flow through the protective circuit. FIG. 12 shows asectional structure of the protective circuit elements constructed tohave a two-stage connection. Over one face of a P-type substrate 61forming an integrated circuit, there is formed an N-type epitaxial layer62. On the surface side of this N-type epitaxial layer 62, there areformed a plurality of (or two, as shown) P-type diffusion layers 63 forwells. In the surface layer portion of the P-type diffusion layer 63, onthe other hand, there is formed an N-type diffusion layer 64. Therefore,the P-type diffusion layer 63 and the N-type diffusion layer 64 form PNjunction diodes (51 and 52).

Between the individual P-type diffusion layers 63, on the other hand,there is formed a P-type insulating diffusion layer 65 as a channelstopper. This P-type isolating diffusion layer 65 so extends all over inthe thickness direction of the N-type epitaxial layer 62 as to reach theP-type substrate 61 at is lower end.

Over the surface on one side of the P-type substrate 61, on the otherhand, there is formed a silicon dioxide film 66. This silicon dioxidefilm 66 is partially removed at its portion confronting the P-typediffusion layer 63 and the N-type diffusion layer 64, to form contactwindows. Over the silicon dioxide film 66 including those contactwindows, moreover, there is formed an aluminum deposited layer 67 in apredetermined pattern.

As a result, the two diodes 51 and 52 are connected in series in theforward direction by the aluminum deposited layer 67, and one diode 51is connected at its cathode electrode 68 with the signal line 53 of theinternal circuit whereas the other diode 52 is connected at its anodeelectrode 69 with the ground line 55.

SUMMARY OF THE INVENTION

In accordance with the miniaturization of the wireless communicationmobile terminal device of recent years, there has been desired anddeveloped a one-chip IC in which the transmission/reception bandmodulator/demodulator circuits and the high-frequency amplifications areintegrated to correspond to the low-noise amplifier 4, the receptionmixer 6, the variable-gain controlled amplifier 8, the demodulator 9,the modulator 11, the variable-gain controlled amplifier 12, thetransmission mixer 13 and the transmission preamplifier 15, as shown inFIG. 9. It is necessary to protect the entire chip against the highbreakdown voltage.

However, it has been found out that the one-chip IC of the prior artincorporating the protective circuit has the following problems.

-   (1) The high-frequency circuit including the low-noise amplifier 4,    the reception mixer 6, the transmission mixer 13 and the    transmission preamplifier 15 is provided at its input/output    circuits with a matching circuit having a capacity and an    inductance. With the inductance of this matching circuit, for    example, a high voltage is generated by the change in the voltage at    the input/output portions of the integrated circuit. Moreover, the    output terminals of the individual circuits are biased in the DC    manner to the potential of the power supply voltage. As a result, in    response to the input signal, a signal having a potential no less    than the power supply voltage is outputted. If the circuit having a    construction of transistors of one stage is applied as the    protective circuit as in the example of the prior art, a bias    condition for allowing the electric current to flow through that    protective circuit is established to raise a problem that the signal    is distorted.-   (2) On the other hand, the attachment of the protective circuit of    the prior art raises a problem that the parasitic capacity is so    high as to deteriorate the gain. This makes it hard to apply the    protective circuit of the prior art to the circuit of the    high-frequency portion.-   (3) In the protective circuit having the transistors of a    construction of two stages of the prior art, on the other hand, the    element structure is constructed of thyristors. If a high static    electricity is applied, therefore, the IC actions cannot be made    because an overcurrent continuously flows unless the power supply is    broken.

The problems, as found out by our investigations to be caused by theprotective circuit for the high-frequency circuit, will be describedwith reference to FIGS. 13A and 13B and the subsequent Figures. First ofall, the deterioration of the linearity will be described in the case ofa circuit output.

FIGS. 13A and 13B illustrate the static characteristics of the NMOStransistors 42 and 43 of FIG. 10 and the actions of the high-frequencysignals. With the circuit construction shown in FIG. 10, in the actionstate in which the power supply of the IC and the ground are connectedwith the power supply line over the substrate, little electric currentflows through the transistors of the protective circuit, but the desiredsignal voltage is applied to the internal circuit 45, when the signalvoltage Vcc desired by the circuit is applied to the signal line 44.

Next, if a positive static electricity V1 higher than the voltage Von,at which the transistors are turned ON, + the power supply voltage Vccare applied to the signal line 44 at the time of handling the IC on thesubstrate, a diode forward current I flows through the NMOS transistor42, as shown in FIG. 13A, but no overcurrent flows through the internalcircuit so that the internal circuit 45 is protected.

Likewise for a high negative static electricity, if an electrostaticvoltage V2′ no higher than −Von is applied, as shown in FIG. 13B, adiode forward current I′ flows through the transistor 43 to protect theinternal circuit 45.

Here, the high-frequency circuit adopts the method the matching is madeby connecting the source terminal directly with the outside of the ICand by using the capacity and the inductance so as to amplify the outputdrastically, the power supply voltage is applied to the IC outputterminal.

The internal circuit 45 of FIG. 10 corresponds to the low-noiseamplifier 4, the reception mixer 6, the transmission mixer 13 or thetransmission preamplifier 15 of FIG. 9, for example. When the powersupply voltage Vcc is applied to the signal line 44 to superpose ahigh-frequency signal, a high-frequency voltage 46 around the graphorigin of FIG. 13A is applied to the transistor 42. If thehigh-frequency voltage amplitude is no more than Von, littlehigh-frequency current flows through the transistor 42, and the currentamplitude of the internal circuit is outputted. If the voltage amplitudebecomes large over Von, however, a nonlinear high-frequency current 47flows to the transistor 42 so that it is superposed on the outputcurrent amplitude of the internal circuit to distort the output signal.

Under this action condition, the input amplitude of the desired wave ofthe reception circuit is at Von or smaller so that the distortion raisesno serious problem. If the interfering wave in the near band, as cannotbe filtered out by the upstream circuit stage, is so large as to have avoltage amplitude at Von or higher, however, the interfering wave causesa distortion to deteriorate the S/N characteristics in the receptionband. In the transmission circuit, on the other hand, the desired wavehas a large output amplitude so that the S/N deterioration occurslikewise at the distortion by the desired wave.

Here will be described the case of the input point of the circuit. Wherethe circuit includes enhancement type transistors such as Si bipolartransistors having a bias voltage at about +1 V at their input points,the protective circuit is normally OFF even if the high-frequencyvoltage amplitude is inputted, so that no electric current flows throughthe protective transistors thereby not to distort the input signal. Inthe case of the depression type such as the GaAs FETs, however, when anegative voltage V3′ is applied to the signal line so that thehigh-frequency signal is superposed, as shown in FIG. 13B, ahigh-frequency voltage 48 around V3′ is applied to the transistor 43. Ifthe high-frequency voltage is no higher than −Von, it hardly flowsthrough the transistor 43 so that the signal is transmitted as it is tothe internal circuit.

If the voltage exceeds the value of −Von to a large amplitude, however,a nonlinear high-frequency current 49 flows through the transistor 43and is superposed over the input current amplitude of the internalcircuit to distort the input signal.

If the input signal has a distortion, this distortion is amplified bythe internal circuit so that the amplified distortion is superposed onthe distortion to be caused in the intrinsic signal, thereby todeteriorate the linearity. Like the aforementioned time of the outputsignal, the S/N ratio is deteriorated. This is because the protectivecircuit for the transistors of one stage diode-connected are provided onthe power supply side and on the ground side for the signal lines.

In order to solve this problem, there is a method in which thediode-connected transistors are connected in series to raise the voltageVon so that little electric current may flow at the desired voltage forthe internal circuit to act, as in the aforementioned protective circuithaving the two-stage construction of FIG. 11. Moreover, the seriesconnection reduces the parasitic capacity and the deterioration in thefrequency characteristics.

According to this structure, however, a portion, as designated by 70 inFIG. 12, is given the thyristor structure by inserting the P-typediffusion layer of the channel stopper. The action principle of thethyristor is shown in FIG. 14. The thyristor is in the turn-OFF state toallow little electric current to flow, when it is in the forward voltagestate and at a low voltage. When the voltage rises high, the thyristoris turned ON to allow a large electric current to flow. Therefore, theprotective circuit of the diode construction having the multistageconnection may be turned ON with a high voltage of static electricity.In order to prevent this, the power supply has to be broken. Thisbreakdown is difficult to realize for the transistor structure of theprior art.

In the construction where the electric current flows from the ground tothe power supply, as shown in FIG. 10, no problem arises, when the powersupply and the ground of the IC are connected with the wiring lines ofthe substrate so that the power is supplied. When the IC is chargedwhile being handled for its assembling work, however, the protectivecircuit may not function. With the IC being in the floating state andwith the ground being open, for example, if a plus (+) or minus (−)potential difference is established between the voltage Vcc and thesignal line 44, the voltage Vcc on the plus side with respect to theminus side of the signal line becomes inverse so that no electriccurrent flows through the protective circuit. In other words, theprotective circuit is weak against the negative static electricity withrespect to the voltage Vcc, and the internal circuit may be broken bythe high negative static electricity.

An object of the invention is to provide a semiconductor integratedcircuit device for wireless communications, which has an electrostaticbreakdown protecting circuit capable of protecting an IC reliablyagainst positive/negative static electricities.

Another object of the invention is to provide a semiconductor integratedcircuit device for wireless communications which has a protectivecircuit capable of protecting a low-frequency circuit (including acircuit of an intermediate-frequency band) and a circuit of ahigh-frequency band against the electrostatic breakdown.

Still another object of the invention is to provide a semiconductorintegrated circuit device for wireless communications, which isexcellent against the electrostatic breakdown while preventing thedeteriorations of the linearity and gain of the high-frequency circuit.

The aforementioned and other objects and novel features of the inventionwill become apparent from the following description to be made withreference to the accompanying drawings.

A representative of the invention to be disclosed herein will be brieflydescribed in the following.

For the circuit (or the low-frequency circuit) of theintermediate-frequency, protective circuits including diode-connectedtransistors of one stage are individually disposed on power supply linesand the ground line. For the circuit of the high-frequency band of theIC, there are incorporated, as the protective circuit having a lowparasitic capacity and little deterioration of signal characteristics,multistage protective circuits in which the voltage Von is not exceededeven when a signal at the power supply voltage or higher is applied, inaccordance with the action point of the applied circuit, and multistageprotective circuits which are not turned ON even when a signal exceedinga negative bias potential is applied. On the other hand, the protectivecircuits are constructed to protect the IC, irrespective of the polarityof the static electricities to be established while the IC is beinghandled. Specifically, the protective circuits include: a firstprotective circuit for allowing an electric current to flow from a powersupply line to signal lines at a protection time against anelectrostatic breakdown; a second protective circuit for allowing anelectric current to flow from the signal lines to the ground line; athird protective circuit for allowing an electric current to flow fromthe signal lines to the power supply line; and a fourth protectivecircuit for allowing an electric current to flow from the ground line tothe signal lines. Moreover, the diode-connected transistors of themultistage connection are given a structure in which the elements (i.e.,the diode-connected transistors) are isolated by an insulator capable ofthe thyristor action.

According to the means thus far described, (a) in the semiconductorintegrated circuit device, each internal circuit of the high-frequencyband is provided at its input/output portions with the protectivecircuit of the multistage structure so that the internal circuit can beprevented from the electrostatic breakdown, as might otherwise be causedby the high positive/negative static electricities. On the other hand,each internal circuit of the low-frequency band is provided at itsinput/output portions with the protective circuit of one stage so thatit can be prevented from the electrostatic breakdown, as might otherwisebeen caused by the positive/negative static electricities.

(b) The output terminal of each internal circuit 29 of thehigh-frequency band is biased to the power supply voltage so that asignal at an output voltage or higher is outputted in response to theinput signal. Where the protective circuit is made of the circuitincluding transistors of one stage construction, as in the prior art,therefore, the bias condition for the electric current to flow throughthe protective circuit is raised to distort the signal. In theinvention, on the contrary, this signal distortion can be suppressedbecause the protective circuit of the multistage structure is adopted.

(c) The transistors are formed in the semiconductor regions which areelectrically insulated from one another, so that the formation of thethyristor, as might otherwise be formed by the two-stage construction oftransistors of the prior art, can be prevented.

(d) The protective circuit, as disposed at the input/output portions ofeach internal circuit of the high-frequency band is constructed toinclude the diode-connected transistors of the multistage structure.Therefore, the parasitic capacity is lowered to reduce the deteriorationof the linearity or the gain of the high-frequency circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a protective circuit to beincorporated into an internal circuit in a semiconductor integratedcircuit device according to one embodiment (Embodiment 1) of theinvention;

FIGS. 2A and 2B are diagrams showing individual current paths at thetimes when the protective circuit, protects electrostatic breakdownscaused by positive/negative static electricities;

FIG. 3 is a circuit diagram showing a circuit in which the protectivecircuit is incorporated into an amplifier circuit as an internalcircuit;

FIG. 4 is a characteristic diagram of the amplifier circuit;

FIG. 5 is a block diagram showing a construction of a wirelesscommunication system having the semiconductor integrated circuit deviceof Embodiment incorporated thereinto;

FIG. 6 is a sectional diagram showing diode-connected transistorsconstructing a protective circuit in the semiconductor integratedcircuit device;

FIG. 7 is a circuit diagram showing a protective circuit to beincorporated into a low-frequency internal circuit of the wirelesscommunication system;

FIG. 8 is a circuit diagram showing a protective circuit to beincorporated into an internal circuit of a semiconductor integratedcircuit device according to another embodiment (Embodiment 2) of theinvention;

FIG. 9 is a block diagram showing a construction of a wirelesscommunication system having the semiconductor integrated circuit deviceincorporated thereinto;

FIG. 10 is a circuit diagram showing a protective circuit;

FIG. 11 is a circuit diagram showing another protective circuit;

FIG. 12 is a schematic sectional diagram showing a transistorconstruction to be used in a protective circuit;

FIGS. 13A and 13B are characteristic diagrams illustrating the staticcharacteristics used in a protective circuit of transistors and theactions of a high-frequency signal; and

FIG. 14 is a schematic diagram showing a structure and an actionprinciple of a thyristor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in detail in connection with itsembodiments with reference to the accompanying drawings. Here,throughout all the Figures for explaining the embodiments of theinvention, the parts having the same functions are designated by thesame reference numerals, and their repeated description will be omitted.

Embodiment 1

FIGS. 1 to 7 are diagrams relating to a semiconductor integrated circuitdevice according to one embodiment (Embodiment 1) of the invention, andFIGS. 1 to 5 are diagrams relating to a protective circuit.

In Embodiment 1, the invention will be described on the example in whichit is applied to a signal processing IC for a cellular phone. Here willbe described a construction of the cellular phone. FIG. 5 is a blockdiagram showing a portion of a system construction of the cellularphone.

In this block diagram, as in FIG. 9, there are shown a transmission lineand a reception line which are connected with an antenna 1 through aduplexer 2. Both of these transmission line and reception line areconnected with a not-shown base band.

The reception line is constructed by connecting the antenna 1, aband-pass filter 3 packaged in the duplexer 2, a low-noise amplifier 4,a band-pass filter 5, a receiving mixer 6, a band-pass filter 7, avariable-gain controlled amplifier 8 and a demodulator 9 sequentially inseries. The demodulator 9 is connected with the not-shown base band.

The transmission line is constructed by connecting a modulator 11, avariable-gain controlled amplifier 12, a transmission mixer 13, aband-pass filter 14, a transmission preamplifier 15, a high-outputamplifier 16, a band-pass filter 17 packaged in the duplexer 2, and theantenna 1 sequentially in series. The modulator 11 is connected with thenot-shown base band. On the other hand, the demodulator 9 and themodulator 11 performs frequency conversions in response to a localoscillation signal inputted from a VCO 18. The reception mixer 6 and thetransmission mixer 13 also perform frequency conversions in response toa local oscillation signal inputted from a VCO 19.

A signal (in electric waves), as received by the antenna 1, issequentially processed by the individual circuit of the reception lineand is set to the base band. On the other hand, a signal sent from thebase band is sequentially processed by the individual circuits of thetransmission line and is emitted as the electric waves 10 from theantenna 1. The signal 10, as emitted from the antenna 1, and the signal10, as received by the antenna 1, are exemplified to have ahigh-frequency band of 1 GH, but signals of a low-frequency band areprocessed by the demodulator 9, the modulator 11 and so on fortransferring signals with the base band. The signals of thelow-frequency band are exemplified to have an intermediate-frequencyband of several hundreds MHz.

In Embodiment 1, the individual circuit elements (of internal circuits)for processing signals, as including the low-noise amplifier 4 aremonolithically packaged in a single semiconductor IC chip 25, asenclosed by solid lines in FIG. 5. In this semiconductor IC chip 25,more specifically, there are monolithically packaged as the internalcircuits the low-noise amplifier 4, the reception mixer 6, thevariable-gain controlled amplifier 8, the demodulator 9, the VCO(Voltage Controlled Oscillator) 18, the modulator 11, the variable-gaincontrolled amplifier 12, the transmission mixer 13, the transmissionpreamplifier 15 and the VCO 19.

At the input/output portions of the semiconductor IC chip 25,respectively, there are provided protective circuits which are made tostand high voltages for preventing the electrostatic breakdowns, asmight otherwise be caused by the electrostatic charges (orpositive/negative static electricities) from several tens to severalhundreds V, of the internal circuits. These protective circuits areexemplified by protective circuits 26 of a multistage structure, inwhich a plurality of diode-connected transistors are connected inseries, for a high-frequency band, and protective circuits 27 of onestage, in which one diode-connected transistor is used, for alow-frequency band or an intermediate-frequency band.

The protective circuit 26 of the multistage structure is disposed at theinput/output portion of each of the low-noise amplifier 4, the receptionmixer 6 and the transmission preamplifier 15, at the input portion ofthe variable-gain controlled amplifier 8, and at the output portion ofthe transmission mixer 13. The protective circuit 27 of the one stage isdisposed at the output portion of the demodulator 9 and at the inputportion of the modulator 11.

Here will be described the protective circuit 26 of the multistagestructure to be disposed at the input/output portions of thehigh-frequency band, with reference to FIGS. 1 to 4.

The protective circuit 26 of the multistage structure is constructed, asshown in FIG. 1 and FIGS. 2A and 2B, by arranging a diode of themultistage structure between a signal line 30, and a power supply line31 and a ground line 32, as connected with an internal circuit 29.Letter V appearing in FIG. 1 designates an input signal or an outputsignal to or from the internal circuit 29 so that it is inputted oroutputted via the signal line 30 to or from the internal circuit 29.

The protective circuit 26 of the multistage structure is constructed, asshown in FIGS. 2A and 2B, of: a first protective circuit A in which anelectric current flows via route (1) from the power supply line 31 tothe signal line 30 at the electrostatic breakdown protecting time; asecond protective circuit B in which an electric current flows via route(2) from the signal line 30 to the ground line 32; a third protectivecircuit C in which an electric current flows via route (3) from thesignal line 30 to the power supply line 31; and a fourth protectivecircuit D in which an electric current flows via route (4) from theground line 32 to the signal line 30. The first protective circuit A andthe second protective circuit B prevent the electrostatic breakdown ofthe internal circuit 29 due to the negative static electricity, and thethird protective circuit C and the fourth protective circuit D preventthe electrostatic breakdown of the internal circuit 29 due to thepositive static electricity.

The diodes constructing the protective circuits are exemplified bydiode-connected bipolar transistors and are kept from causing thethyristor phenomenon by the later-described structure.

The third protective circuit C is given a multistage structure in whicha plurality of bipolar transistors 1211 to 121 n all diode-connected byshorting their bases and emitters are connected in series. Thetransistor 1211 at the first stage is connected at its collector with apower supply Vcc (or the power supply line 31) and at its emitter withthe collector of the transistor at the downstream stage. The transistor121 n at the n-th stage is connected at its collector with the emitterof the transistor at the upstream stage and at its emitter with thesignal line 30. Each transistor at the (n−1)-th stage from the secondstage is connected at its collector with the emitter of the transistorat the upstream stage and at its emitter with the collector of thetransistor at the downstream stage.

The fourth protective circuit D is given a multistage structure in whicha plurality of bipolar transistors 1221 to 122 m all diode-connected byshorting their bases and emitters are connected in series. Thetransistor 1221 at the first stage is connected at its collector with asignal line 30 and at its emitter with the collector of the transistorat the downstream stage. The transistor 122 m at the m-th stage isconnected at its collector with the emitter of the transistor at theupstream stage and at its emitter with the ground (or the ground line32). Each transistor at the (m−1)-th stage from the second stage isconnected at its collector with the emitter of the transistor at theupstream stage and at its emitter with the collector of the transistorat the downstream stage.

By thus raising the Von of the transistors 1211 to 121 n connected withthe power supply, the transistors are turned OFF at a desired activevoltage of the internal circuit 29 so that no electric current may flow.By likewise lowering the −Von of the transistors 1221 to 122 m connectedwith the ground, the transistors are turned OFF at a desired activevoltage of the internal circuit 29 so that no electric current may flow.

The first protective circuit A is connected in parallel with the thirdprotective circuit C and is formed of a breakdown protective circuit anddiodes of a multistage connection structure. Specifically, the firstprotective circuit A is constructed to include: a MOS transistor 1231constructing the breakdown protective circuit between the power supplyVcc (or the power supply line 31) and the signal line 30; and aplurality of bipolar transistors 1241 to 124 i connected between the MOStransistor 1231 and the signal line 30. These transistors 1241 to 124 ihaving a structure, in which bases and emitters are all diode-connected,and are connected in series with one another to make the multistagestructure as a whole.

The MOS transistor 1231 is connected at its drain (or its one electrode)connected with the power supply line 31, at its source (or its otherelectrode) with the emitter of the first-stage transistor 1241, and atits gate with the ground line 32. The collector of the transistor 1241at the first stage is connected with the emitter of the transistor atthe downstream stage. The transistor 124 i at the i-th stage isconnected at its emitter with the collector of the transistor at the(i−1)-th stage and at its collector with the signal line 30. Eachtransistor at the (i−1)-th stage from the second stage is connected atits emitter with the collector of the transistor at the upstream stageand at its collector with the emitter of the transistor at thedownstream stage.

The second protective circuit B is connected in parallel with the fourthprotective circuit D and is formed of a breakdown protective circuit anddiodes of a multistage connection construction. Specifically, the secondprotective circuit B is constructed to include: a plurality of bipolartransistors 1251 to 125 k having bases and emitters diode-connectedbetween the signal line 30 and the ground line 32 (or the ground) andconnected in multiple stages in series; and a MOS transistor 1261connected between the collector of the transistor 125 k and the groundline 32 to construct the breakdown protective circuit. The MOStransistor 1261 is connected at its drain (or its one electrode) withthe collector of the transistor 125 k and connected at its gate andsource (or its other electrode) with the ground line 32.

In the protective circuit 26 thus constructed, when the semiconductor ICchip 25 is handled, the paths of the electrostatic currents at theindividual potential differences in the power supply line, the groundline and the signal line are shown in FIGS. 2A and 2B. For conveniencesof the description, the first protective circuit A and the secondprotective circuit B are constructed to include transistors of onestage, and the third protective circuit C and the fourth protectivecircuit. D are constructed to include transistors of two stages. Theseindividual transistors are simply shown as diodes.

FIG. 2B shows the potential relations among the power supply (Vcc), theground (GND) and the signal line (S), and which of the current paths (1)to (4) the electric current flows through in the circuits. The MOStransistor allows the electric current to flow by the punch through orthe source-follower when a high static electricity is applied. Asapparent from FIG. 2B, a current path is at any potential difference atany portion so that no overcurrent flows through the internal circuit29.

If it is considered that a desired positive voltage is applied to theinternal circuit 29, on the other hand, the transistors 1221 to 122 mand transistors 1241 to 124 i are reversely biased to cause nounnecessary leakage current to the power supply. The transistors 1211 to121 n are not turned ON either at a voltage of (Vcc+Von×n) or lower. Noris caused the punch-through by the transistor 1261 at the desiredvoltage so that no leakage occurs to the ground.

Where the desired voltage is negative, the transistors 1251 to 125 k andthe transistors 1211 to 121 n are reversely biased. The transistors 1221to 122 m are not turned ON either up to −Von×m. Nor flows the electriccurrent through the MOS transistor 1231. Therefore, the signal iscorrectly transmitted between the internal circuit 29 and the terminal(V).

These bipolar transistor is given a structure, as shown in FIG. 6. Thebipolar transistor is formed over an SOI (Silicon On Insulator)substrate 71 which is prepared by laminating an insulator such as asilicon dioxide layer 73 over a silicon substrate 72. Over the SOIsubstrate 71, there is formed an N-type epitaxial layer 74. In thisN-type epitaxial layer 74, there are selectively formed endless groovesby the dry-etching method or the like. These groove extend so far as toreach the silicon dioxide layer 73. Moreover, the grooves are filledwith an insulator 75. For example, the grooves are filled with silicondioxide by the CVD (Chemical Vapor Deposition) method. Therefore, theN-type epitaxial layer 74, as enclosed by the insulator 75, is anelectrically independent region. In this region, there is formed thetransistor.

In the surface layer portion of the N-type epitaxial layer 74 enclosedby the insulator 75, there is formed a P-type diffusion layer 76. Thisregion is employed as the base region. In the surface layer portions ofthe P-type diffusion layer 76 and the N-type epitaxial layer 74, thereare formed N-type diffusion layers 77 and 83. The region 77 is employedas the collector region. The N-type diffusion layer 83, as formed in thesurface layer portion of the P-type diffusion layer 76, is the emitterregion.

Over the N-type epitaxial layer 74, the insulator 75, the P-typediffusion layer 76 and the N-type diffusion layers 77 and 83, on theother hand, there is formed a silicon dioxide layer 78. This silicondioxide layer 78 is partially removed at the portions confronting theemitter/base/collector regions to form contact holes. In the regionsincluding these contact holes, moreover, wiring lines are formed in apredetermined pattern. These wiring lines form a collector electrode 80,a base electrode 81 and an emitter electrode 82.

Thus, the silicon dioxide layer 73 and the insulator 75 are used asbarriers to form transistors which are so electrically isolated from oneanother as to form no thyristor. In FIG. 6, the emitter electrode 82 andthe base electrode 81 are connected by a wiring line 79 to make a diodeconstruction, and these constructions are connected at multiple stagesin series to construct the protective circuit. Although the bipolartransistors have been exemplified in the description thus far made, asimilar electrically insulating structure (or an isolation structure) isalso used when a MOSFET is constructed. The structure of this transistoris applied to the MOS transistor 1231 in the IC circuit. FIG. 7 is acircuit diagram showing the aforementioned protective circuit 27 of onestage. In FIG. 7, the protective circuit A is constructed of the MOStransistor 1231 forming the breakdown protective circuit. This MOStransistor 1231 is connected at its drain with the power supply line 31,at its source with the signal line 30 and at its gate with the groundline 32. This breakdown protective circuit can be deemed as a protectivecircuit of a source-follower transistor.

The second protective circuit B, as shown in FIG. 7, has the MOStransistor 1261 constructing the breakdown protective circuit, and thisMOS transistor 1261 is connected at its drain with the signal line 30and at its source with the ground line 32. This breakdown protectivecircuit can be deemed as a protective circuit of the surface breakdown.

The third protective circuit C is constructed of the bipolar transistor1211. This transistor 1211 is connected at its collector with the powersupply line 31 and at its emitter with the signal line 30.

The fourth protective circuit D is constructed of the bipolar transistor1221. This transistor 1221 is connected at its collector with the signalline 30 and at its emitter with the ground line 32.

This protective circuit 27 of the one stage prevents the damage of theinternal circuit 29 due to the positive/negative static electricitieslike the aforementioned protective circuit 26 of the multistagestructure.

Here will be described a more specific example of the circuitconstruction of the invention. This embodiment is especially effectivewhen the integral circuit is constructed of a BiCMOS (BiP transistor, aP-type MOS transistor or an N-type MOS transistor).

FIG. 3 shows one example of the case in which a high-frequency amplifiercorresponding to the low-noise amplifier 4 of FIG. 5 is applied as theinternal circuit and in which the protective circuit of the invention isdisposed at the output stage. A portion 90, as enclosed by a frame, is acircuit in the IC containing the protective circuit. Circuits 95 and 96outside of the IC are input and output matching circuits, respectively.The amplifier is a current-mirror type amplifier which is fed with avoltage Vb to feed a constant current to a transistor 93 and which isfed with a high-frequency input voltage Vin to output a signal at anamplified voltage Vout. In the circuit diagram, a portion 91 is aprotective circuit which is constructed to include transistors 92 a to92 i having the structure shown in FIG. 6 and isolated electrically fromone another. The internal transistor 93 is fed at its collector 94 withthe same voltage of 3 V as the power supply voltage via the inductor ofthe output matching circuit 96. If the protective circuit has only thetransistor 92 a of one stage, there appears at the collector terminal 94a superposition of a forward current, which flows from the protectivecircuit to the power supply voltage of 3 V in accordance with thecharacteristics of the exponential function of the bipolar transistor,and an amplifier output current which is generated by the transistor 93.The voltage amplitude of the amplifier raises no problem, when it isextremely small, but the nonlinear current to flow through thetransistor of the protective circuit increases to cause a distortion asthe amplitude becomes large. In order that the voltage Von at which thetransistor in the protective circuit begins to become conductive may beat 4 V as the voltage capable satisfying the dynamic range of theamplifier, the transistors of the protective circuit are connected atthree stages in series to establish no electric flow at the circuitaction point. The circuit of the example needs no negative power supply.By making the transistor of one stage to be connected with the ground,therefore, the circuit is protected even if a low negative staticelectricity is applied. By this protective circuit, moreover, the IC isprotected, as described above, even the static electricity isestablished at the time of handling the IC.

FIG. 4 plots the input/output characteristics of the amplifiers when thetransistors to be connected with the power supply in the protectivecircuit are stacked at one stage and at three stages. As apparent fromFIG. 4, the one-stage series connection is changed to the three-stageseries connection, the compression point of 1 dB is changed from −15 dBmto −8 dBm so that the linearity is improved. Since the collector-emittercapacity of the individual transistors are connected in series,moreover, the parasitic capacity of the protective circuit is reduced,as compared with that of the protective circuit of the prior art whichis constructed to include transistors of one stage diode-connectedindividually with the power supply and the ground, so that the gain ofthe amplifier is less deteriorated. The circuit for theintermediate-frequency band has such a low frequency that thecharacteristic deterioration due to the parasitic capacity is remarkablysmall even in the protective circuit of the prior art. On the otherhand, the adjoining transistors are isolated by the insulator or thesilicon dioxide layer so that they do not act as the thyristor.

The description thus far made is exemplified by the output point of theenhancement type transistor. In the case of the depression typetransistor input as in a GaAs FET, however, a nonlinear current issuperposed on the input signal and is amplified to deteriorate thelinearity likewise, if the voltage of −Von of the transistor to beconnected with the ground is higher than the voltage to be applied tothe gate of the transistor. This makes it necessary to provide such aprotective circuit on the input side, too, that the transistors to beconnected with the ground are connected in series to lower the voltageof −Von. Thus, the number of series of the transistors is determined bythe action point of the internal circuit and by the target value of thecompression point of 1 dB.

The semiconductor integrated circuit device of Embodiment 1 has thefollowing effects.

-   (1) In the semiconductor integrated circuit device, each internal    circuit 29 of the high-frequency band is provided at its    input/output portions with the protective circuit 26 of the    multistage structure so that the internal circuit 29 can be    prevented from the electrostatic breakdown, as might otherwise be    caused by the high positive/negative static electricities. On the    other hand, each internal circuit of the low-frequency band is    provided at its input/output portions with the protective circuit 27    of one stage so that it can be prevented from the electrostatic    breakdown, as might otherwise been caused by the positive/negative    static electricities.

Here, if the protective circuits of the high-frequency circuit portionare connected in series, as described hereinbefore, the voltage Vonrises so that the current hardly flows to lower the electrostaticbreakdown, as compared with the protective circuits of theintermediate-frequency band. However, the electrostatic voltage to breakthe IC (or the internal circuit) is at a level of several tens toseveral hundreds V, which is far higher than that of the IC to act atsuch a low power supply voltage as the invention is applied to.Therefore, a slight reduction in the breakdown voltage, as caused byraising the voltage Von, raise no problem.

-   (2) The output terminal of each internal circuit 29 of the    high-frequency band is biased to the power supply voltage of a DC    value so that an output voltage according to the input signal is    produced at the output terminal. This output voltage is changed    around the bias voltage (at about the power supply voltage) by the    inductance connected with the output terminate. Where the protective    circuit is made of the circuit including transistors of one stage    construction, as in the prior art, therefore, the bias condition for    the electric current to flow through the protective circuit is    raised to distort the signal. In the invention, on the contrary,    this signal distortion can be suppressed because the protective    circuit of the multistage structure is adopted.-   (3) The transistors are formed in the semiconductor regions which    are electrically insulated from one another, so that the formation    of the thyristor, as might otherwise be formed by the two-stage    construction of transistors of the prior art, can be prevented.-   (4) The protective circuit, as disposed at the input/output portions    of each internal circuit 29 of the high-frequency band is    constructed to include the diode-connected transistors of the    multistage structure. Therefore, the parasitic capacity is lowered    to deteriorate neither the linearity nor the gain of the    high-frequency circuit.-   (5) The two kinds of protective circuits, i.e., the protective    circuit 26 of the multistage structure and the protective circuit 27    of the one stage are disposed in the one-chip IC so that a high    breakdown voltage can be established against the electrostatic    breakdown of the entirety.

Embodiment 2

FIG. 8 shows a protective circuit of a semiconductor integrated circuitdevice according to another embodiment (Embodiment 2) of the invention.In the aforementioned protective circuit of the multistage structure ofEmbodiment 1 shown in FIG. 1, the bipolar transistors are replaced asthe diode-connected transistors by MOSFETs in accordance with Embodiment2. These MOSFETs are diode-connected by shorting their gates andsources.

The first protective circuit A is constructed to include: a MOSFET(transistor) 4331 connected between the power supply line 31 and thesignal line 30 for forming a breakdown protective circuit; and aplurality of MOSFETs 4341 to 434 i connected between the MOSFET(transistor) 4331 and the signal line 30. The second protective circuitB is constructed to include: a plurality of MOSFETs (transistors) 4351to 435 k connected in series at multiple stages between the signal line30 and the ground line 32; and a MOSFET (transistor) 4361 connected withthe MOSFET 435 k for forming a breakdown protective circuit. The thirdprotective circuit C is constructed to include a plurality of MOSFETs(transistors) 4311 to 431 n connected in series. The fourth protectivecircuit D is constructed to include a plurality of MOSFETs (transistors)4321 to 432 m connected in series.

In the protective circuit 26 of the multistage structure thusconstructed, too, the electrostatic breakdown of the internal circuit29, as might otherwise be caused by the positive/negative staticelectricities, can be prevented as in Embodiment 1.

Although our invention has been specifically described on the basis ofits embodiments, it should not be limited thereto but could naturally bemodified in various manners without departing from the gist thereof.

The description thus far made is directed mainly to the case in whichour invention is applied to the semiconductor integrated circuit deviceto be incorporated into the wireless communication system belonging tothe application field backgrounding the invention, but the inventionshould not be limited thereto. The invention can be applied to thesemiconductor integrated circuit device for processing the signals.

The effects to be obtained by the representative of the inventiondisclosed herein will be briefly described in the following.

-   (1) In the one-chip IC integrating the high-frequency band and the    intermediate-frequency band, according to the invention, the    high-frequency circuit is provided with the protective circuits    connected at multiple stages and in series, in addition to the    protective circuit which is applied to the intermediate-frequency    band and which is constructed to include diode-connected transistors    of one stage of the prior art, so that the parasitic capacity can be    lowered while raising the voltage Von to prevent the deterioration    of the gain or the linearity.-   (2) By thus providing the IC chip with two kinds of protective    circuits of different structures as the individual circuits therein,    on the other hand, the total area of the protective circuits in the    chip can be made smaller than that of the structure in which the    protective circuits of the multistage connection are applied to all    the circuits in the IC.-   (3) Thus, it is possible to realize the high breakdown voltage of    the entire IC against the static electricity.-   (4) It is possible to provide a semiconductor integrated circuit    device for wireless communications, which has an electrostatic    breakdown protecting circuit capable of protecting the IC against    the positive/negative static electricities.-   (5) It is possible to provide a semiconductor integrated circuit    device for wireless communications, which has a protective circuit    capable of protecting a low-frequency circuit (including a circuit    of an intermediate-frequency band) and a circuit of a high-frequency    band against the electrostatic breakdown.-   (6) It is possible to provide a semiconductor integrated circuit    device for wireless communications, which is so excellent against    the electrostatic breakdown that it does not deteriorate the    linearity and gain of the high-frequency circuit.

1. A wireless communication mobile terminal apparatus, comprising: anantenna; a transmitting circuitry including a transmission modulator towhich transmission base band signals and transmission intermediatefrequency local signals are supplied and which outputs a transmissionintermediate frequency output signal and a transmission frequencyconversion circuit to which the transmission intermediate frequencyoutput signal and a transmission radio frequency local signal aresupplied; a receiving circuitry, processing a radio frequency inputsignal received by the antenna and outputting reception base bandsignals, including a reception demodulator which responds to the radiofrequency input signal received by the antenna and a reception localsignal and a low noise amplifier for receiving and amplifying the radiofrequency input signal received by the antenna; and a radio frequencypower amplifier which amplifies an output of the transmission frequencyconversion circuit and outputs to the antenna, wherein the transmittingcircuitry and the receiving circuitry are monolithically integrated on asilicon semiconductor chip, wherein a protective circuit is alsomonolithically integrated on the silicon semiconductor chip and arrangedbetween the antenna and the low noise amplifier so that the protectivecircuit is prevented from suffering from electrostatic breakdown of thelow noise amplifier, wherein the semiconductor chip includes a firstvoltage line which is supplied with a first voltage (VCC) and a secondvoltage line which is supplied with a second voltage (GND) lower thanthe first voltage, wherein the protective circuit which is arrangedbetween the first voltage line and the second voltage line and whichincludes a signal node which receives the high frequency signal, a firstprotection unit (A) which allows an electric current flow from the firstvoltage line to the signal node and a second protection unit (B) whichallows an electric current flow from the signal node to the secondvoltage line, a third protection unit (C) which allows an electriccurrent flow from the signal node to the first voltage line and a fourthprotection unit (D) which allows an electric current flow from thesecond voltage line to the signal node, wherein the first protectionunit includes a first protection circuit and a plurality of first diodeswhich are connected in series and arranged between the first voltageline and the signal node, and wherein the second protection unitincludes a second protection circuit and a plurality of second diodeswhich are connected in series and arranged between the signal node andthe second voltage line.
 2. A semiconductor integrated circuit deviceaccording to claim 1, wherein the third protection unit (C) includes aplurality of third diodes which are connected in series and arrangedbetween the signal node and the first voltage line, wherein the fourthprotection unit (D) includes a plurality of fourth diodes which areconnected in series and arranged between the second voltage line and thesignal node, wherein the first protection unit (A) and the thirdprotection unit (C) are arranged in parallel between the first voltageline and the signal node, wherein the second protection unit (B) and thefourth protection unit (D) are arranges in parallel between the signalnode and the second voltage line.
 3. A semiconductor integrated circuitdevice according to claim 2, wherein a parasitic capacitance of theprotective circuit is adapted to the low noise amplifier so that acharacteristic of the low noise amplifier is less deteriorated.
 4. Asemiconductor integrated circuit device according to claim 1, whereinthe receiving circuitry further includes a reception frequencyconversion circuit to which the amplified radio frequency output signalfrom the low noise amplifier and a reception transmission radiofrequency local signal are supplied, the reception frequency conversioncircuit also being monolithically integrated on the siliconsemiconductor chip, and wherein the reception demodulator is suppliedwith a converted reception intermediate frequency signal from an outputof the reception frequency conversion circuit and with the receptionlocal signal of an intermediate frequency.
 5. A wireless communicationmobile terminal apparatus, comprising: an antenna; a transmittingcircuitry including a transmission modulator to which transmission baseband signals and a transmission local signal are supplied, a receivingcircuitry including a low noise amplifier for receiving and amplifyingthe radio frequency input signal received by the antenna and a receptiondemodulator which responds to an output of the low noise amplifier and areception local signal and; and a radio frequency power amplifier whichamplifies an output of the transmission frequency conversion circuit andoutputs to the antenna, wherein a protective circuit is alsomonolithically integrated on the silicon semiconductor chip and arrangedbetween the antenna and the low noise amplifier so that the protectivecircuit is prevented from suffering from electrostatic breakdown of thelow noise amplifier, wherein the semiconductor chip includes a firstvoltage line which is supplied with a first voltage and a second voltageline which is supplied with a second voltage lower than the firstvoltage, wherein the protective circuit which is arranged between thefirst voltage line and the second voltage line and which includes asignal node which receives the high frequency signal, a first protectionunit which allows an electric current flow from the first voltage lineto the signal node and a second protection unit which allows an electriccurrent flow from the signal node to the second voltage line, a thirdprotection unit which allows an electric current flow from the signalnode to the first voltage line and a fourth protection unit which allowsan electric current flow from the second voltage line to the signalnode, wherein the first protection unit includes a first protectioncircuit and a plurality of first diodes which are connected in seriesand arranged between the first voltage line and the signal node, andwherein the second protection unit includes a second protection circuitand a plurality of second diodes which are connected in series andarranged between the signal node and the second voltage line.
 6. Asemiconductor integrated circuit device according to claim 5, whereinthe third protection unit (C) includes a plurality of third diodes whichare connected in series and arranged between the signal node and thefirst voltage line, wherein the fourth protection unit (D) includes aplurality of fourth diodes which are connected in series and arrangedbetween the second voltage line and the signal node, and wherein thefirst protection unit (A) and the third protection unit (C) are arrangedin parallel between the first voltage line and the signal node, whereinthe second protection unit (B) and the fourth protection unit (D) arearranged in parallel between the signal node and the second voltageline.